Interactive Energy Diagram and Spectroscopic Model for Solar Water Splitting
Juergen O. Schumacher a, Peter Cendula a, Matthias Schmid a, Michael Graetzel b, Ludmilla Steier b, David Tilley b, Sixto Gimenez c, Juan Bisquert c
a Institute of Computational Physics, Zurich University of Applied Sciences, Wildbachstrasse, 21, Winterthur, Switzerland
Oral, Peter Cendula, presentation 013
Publication date: 31st March 2013

Numerical simulation is crucial for an improved understanding of photoelectrochemical (PEC) cells and for the model-based characterization of appropriate materials. We recently developed and implemented a model to calculate the energy diagram of a PEC cell. The software allows to analyze the energy alignment at the semiconductor/electrolyte interface in the PEC cell. Input parameters of the model are: the semiconductor type, bandgap energy, flatband potential, doping concentration, applied bias, illumination intensity, diffusion length and lifetime of charge carriers. These input parameters can be interactively changed. The effect of the input parameters on the quasi-Fermi levels position with respect to the oxidation and reduction potentials can be deduced. Our energy diagram tool improves the understanding of PEC cells for various materials and can be used freely online at to provide accurate energy diagram plots for future PEC research.

To characterize the charge transfer rate across the semiconductor-liquid junction, methods such as impedance spectroscopy or transient absorption spectroscopy are employed. We provide a simple physical model of charge transfer from semiconductor surface states to the electrolyte or recombination from surface states with conduction band electrons. The impedance spectra are calculated as linear perturbation of the steady-state solution and they enable extraction of the rate constants for charge transfer. Furthermore, our model can be easily extended to describe photocurrent transients and light- or potential-modulated measurements.

Snapshot of the energy diagram of a PEC cell with n-type hematite (implemented in Mathematica). Material parameters can be interactively changed to see their effect on the band edge positions.
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